Method and apparatus for continuous casting with gyrating mold

ABSTRACT

A method and apparatus for continuous casting of an ingot from a molten metal employing a mold having a conical opening passing vertically through it and a mechanism for gyrating the mold about a point without rotating the mold about a vertical axis. The rate of gyration of the mold is related to the rate of continuous withdrawal of the ingot from the mold.

United States Patent Wang 51 June 13, 1972 [54] METHOD AND APPARATUS FOR[56] References Cited CONTINUOUS CASTING WITH UNITED STATES PATENTSGYRATING MOLD 1,010,851 12/1911 Bruckmann ..l64/260 72 Inventor: ChihChung Wang, Lexington M 2,410,837 1 H1946 Peters ..l64/83 3,528,4829/1970 Fastert ..l64/260 [73] Assignee: Kennecott Copper Corporation,New

York, Primary Examiner-Robert D. Baldwin AItorneyJohn L. Sniado, LowellH. McCarter and Kenway, [22] Filed; Dec. 17, I970 Jenney& Hildrelh 211App]. No.: 99,076 [57] ABSTRACT A method and apparatus for continuouscasting of an ingot [52] US. Cl ..164/83, 164/260 f a mohen meta]empbying a mold having a conic opcm [51] Int. Cl. ..B22d 11/02, B22d27/08 ing passing vertically through it and a mechanism for gyrating[58] Field of Search 164/83, 260 the mold about a point without rotatingthe mold about a vertical axis. The rate of gyration of the mold isrelated to the rate of continuous withdrawal of the ingot from the mold.

9 Claims, 3 Drawing Figures PATENTEnJun 13 m2 3.669.182

SHEET 10F 2 INVENTOR CHIH CHUNG WANG BY ATTORN EYS PATENTEnJu'n 13 m2 3.669. 182 sum 2 [IF 2 MOTOR :41

I, INVENTOR CHIH CHUNIG WANG ATTORNEYS METHOD AND APPARATUS FORCONTINUOUS CASTING WITH GYRATING MOLD FIELD OF THE INVENTION BACKGROUNDOF THE INVENTION The present techniques used for continuous casting ofmetal ingots does not present an entirely satisfactory result. In atypical continuous casting process, the liquid melt is fed continuouslyfrom above into the pool and the cast ingot moves downward insynchronization with the feed rate. The ingot is formed in a generallycylindrical open-ended mold. One problem in the usual process arisesfrom rupturing of the ingot, which allows molten metal to flow throughthe fissures into gaps which may exist between the ingot and the mold.This escaped metal solidifies and thereby causes defects on the surfaceof the ingot and increases friction as the ingot is being withdrawn. Onemethod of obviating this difficulty has been to introduce verticalreciprocal motion of the mold as the ingot is being withdrawn. Thevelocity of reciprocation of the mold is related to the velocity ofwithdrawal of the ingot. On the downward stroke the mold is moving inthe same direction as the ingot and thus there is little or no relativevelocity between them and the skin rupture problem is eliminated. On theupward stroke, however, the relative movement between the ingot and themold may increase to values of three times the ingot withdrawal rate andin this portion of the cycle ruptures may still occur.

SUMMARY OF THE INVENTION In the continuous casting process of thisinvention a mold having a conical opening through it is employed. Theconical mold is disposed generally in a position so that the opening isvertical. The molten metal is fed from above into the mold with theingot being formed within the mold and withdrawn at a steady rate fromthe bottom of the mold. A mechanism is provided to gyrate the cone abouta gyration point located on the axis of the cone. The mold does notrotate about the cone axis. As the mold gyrates about the gyrationpoint, that side which is aligned with the vertical axis of the ingotmoves downward simultaneously with the withdrawal of the ingot. Thepitch of the mold opening and the rate of gyration of the mold areselected so that the velocity of this downward vertical movement of themold is matched to the withdrawal velocity of the ingot and hence thereis no relative movement between the two.

On the opposite side of the mold where the mold wall is tilted by thegyration, there is upward movement of the mold. However, because of theconical shape this portion of the mold wall is moving not only upwardbut also outward from the ingot wall, thereby substantially eliminatingfriction between the two. Critical factors in this casting arrangementare the rate of gyration and the gyration point of the cone with respectto the position of the melt level in the ingot. If the rate of gyrationis too fast, a downward compressing force may be exerted on the ingotskin. On the other hand, if the rate of gyration is too slow in relationto the ingot withdrawal speed, the meniscus of the liquid may become toohigh to be supported by the surface tension of the melt and thus spillover. The melt level should be held below the gyration point of the conein order to ensure that the ingot diameter remains constant. However, ifthe melt level is too far below the gyration point then the rotationalsliding of the surface of the mold on the ingot may become excessive.

DESCRIPTION OF THE DRAWINGS In the drawing,

FIG. 1 is an illustration generally in diagrammatic form of a castingapparatus suitable for use in the practice of this invention;

FIG. 2 is an-illustration in vertical cross-sectional view of acontinuous casting apparatus suitable for use in the practice of thisinvention; and

FIG. 3 is a horizontal cross-sectional view taken along the line 3--3 ofFIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to FIG. 1, thereis illustrated a continuous casting apparatus in accordance with thisinvention. A cone shaped mold 11, typically formed of copper, is open ateither end and, in the casting process, a cast ingot 13 is withdrawnfrom the lower end of the mold at a constant rate. The ingot is formedby the solidification of a melt portion 15 within it, which melt isbeing continuously supplied molten metal through a feed 18. The coolingprocess in the ingot 13 is aided by water jets 23 positioned below themold. The top of the melt 15 is definedby a meniscus 17 within the mold.The mold 11 is arranged to gyrate about a gyration point 28 located onthe cone axis without rotation about the axis of the cone by means of agyrating mechanism shown illustratively as wheel 20. As the wheel 20traverses a circular path on the frame surface 12 beneath the peripherallower edge of the mold 11, it produces the gyration to the mold. Thusone portion of the mold wall, shown generally as 25 is, at one time,aligned vertically with the ingot, while the opposite wall 27 of themold is tilted away from the ingot.

If the rate of gyration with respect to the rate of withdrawal of theingot produced by rollers 16 is properly arranged, then the downwardmotion of the vertical side 25 will match in velocity the downwardmovement of the ingot 13, so that there is no relative motion betweenthem. On the opposite side 27 of the mold, the upward movement of themold does not introduce friction between it and the ingot 13 wallbecause the wall 27, being tilted, does not come in sliding contact withthe ingot at this point. The mold illustrated in phantom shows theopposite position during gyration with the wheel 20 located away fromits initial position. As the wheel circles under the mold each portionof the mold is raised and lowered in similar fashion to the portionsindicated as 25 and 27 in FIG. 1. The relationship between the coneangle, the rate of withdrawal and the rate of gyration can be expressedas follows:

R=2 G D tan 0 where,

R= rate of ingot withdrawal in inches/minute G rate of mold gyration inrpm D= diameter of mold opening in inches 0 cone angle.

In a typical example for a small ingot production, a mold inner diameterof r inch with a cone angle of 2 would be operated with a gyration rateof 200 r m and therefore a rate of ingot withdrawal of 7 inches perminute. In general the cone angles of the mold would be expected to bein the range of from about 1 to 4.

In FIGS. 2 and 3 there is illustrated in cross-sectional views acontinuous casting apparatus suitable for use in this invention. Theapparatus includes a mold element 30, which normally would be formed ofcopper and which has a generally cylindrical form, but wherein the bore30a of the mold has a taper between 1 and 4 to form a generally conicalshaped opening through it. The lip 32 at the top of the mold 30 isattached to a retaining flange 31, the latter being supported on abearing 33. The bearing 33 is itself supported on a flanged collar 35which includes an upstanding portion 38 retaining the bearing 33, ahorizontal ring cam surface 37 and a lower collar 36 which bears againsta lower bearing; 39 for rotation with respect to the fixed base 29. Thecam surface 37 is tapered so that upon rotation with respect to the base29 the bearing 33 and hence the supported mold 30 wobble about a point56 on the cone axis introducing the gyration required. A vertical post44 attached to the base 29 secures a horizontally extending arm 45 fromthe flange 31 of the mold to prevent the mold from rotating about anaxis.

A motor 57 drives a circular gear 42 which meshes with a ring gear 40attached to the flanged collar 35 to produce rotation of this flange andits cam surface and hence produce gyration of the mold. A water coolingcoil 48 surrounds the bore 30a of the mold 30 to aid in the solidifyingprocess. The ingot 50, cast in the mold, is withdrawn downwardly fromthe mold 30 through a pair of idler rollers 51 and this withdrawingmotion is imparted to the ingot 50 by means of a driving roller 52. Theroller 52 is driven by a motor 55 and, as earlier indicated, therelative speeds of the withdrawing roller and the rotating cam arearranged to control the rate of gyration with respect to both the taperof the mold and the rate of withdrawal.

What is claimed is: l. A method of continuous casting of a metal ingotfrom a Supply of molten metal comprising the steps of,

gyrating about a point a mold having a vertical cone shaped openingthrough it, said gyration continuously aligning a portion of the moldside with the vertical axis of the ingot,

continuously supplying molten metal into the top of the opening throughsaid mold while withdrawing the solidified ingot from the bottom openingof said mold at a predetermined rate, and

maintaining the downward vertical movement velocity of said portion ofthe mold side matched to said predetermined withdrawal rate whiletilting a portion of the opposite mold side out of sliding contact withsaid ingot.

2. A method in accordance with claim 1 wherein the conical openingthrough said mold has a cone angle and wherein the rate of ingotwithdrawal is expressed as,

R 2 G D tan 6 where,

R rate of ingot withdrawal in inches/minute G rate of mold gyration inrpm D diameter of mold opening in inches 0 cone angle.

3. A method in accordance with claim 1 wherein said molten metal formswithin said ingot a melt having a meniscus level defining its uppersurface and wherein the point of gyration of said mold is above saidmeniscus.

4. Apparatus for continuous casting of metal ingot from molten metalcomprising,

a mold element having a conical opening extending through means forgyrating said mold element about a point on the axis of said conicalopening, such that a portion of the mold side will be continuouslyaligned with the vertical axis of the ingot means for continuoussupplying said molten metal to one end of the opening through said moldelement, and

means for withdrawing continuously at a predetermined rate thesolidified ingot from the other end of the opening through said moldelement such that said ingot withdrawal velocity is matched to thedownward vertical movement velocity of said portion of the mold side.

5. Apparatus in accordance with claim 4 wherein said mold element isformed of copper and is water cooled.

6. Apparatus in accordance with claim 4 wherein said mold element isconstrained from rotating about the axis of said conical opening whensaid element is gyrating.

7. Apparatus in accordance with claim 4 wherein said mold element ispositioned so that said conical opening is generally vertical.

8. Apparatus in accordance with claim 4 and further including meanscontrolling the rate of gyration of said mold element to a firstvelocity and controlling the rate of withdrawal of said ingot, saidmeans for controlling being arranged so that the relationship betweenthe rate of withdrawal of said ingot and the rate of gyration of saidmold is R= 2 G D tan 0 where,

R= rate of ingot withdrawal in inches/minute G= rate of mold gyration inrpm D= diameter of mold opening in inches 0= cone angle.

9. Apparatus in accordance with claim 4 and further including a basemember, said means for gyrating said mold element comprising a rotatablecam element of varying thickness supporting said mold element upon saidbase element and, means for rotating said cam thereby producing thegyration of said mold.

1. A method of continuous casting of a metal ingot from a supply ofmolten metal comprising the steps of, gyrating about a point a moldhaving a vertical cone shaped opening through it, said gyrationcontinuously aligning a portion of the mold side with the vertical axisof the ingot, continuously supplying molten metal into the top of theopening through said mold while withdrawing the solidified ingot fromthe bottom opening of said mold at a predetermined rate, and maintainingthe downward vertical movement velocity of said portion of the mold sidematched to said predetermined withdrawal rate while tilting a portion ofthe opposite mold side out of sliding contact with said ingot.
 2. Amethod in accordance with claim 1 wherein the conical opening throughsaid mold has a cone angle theta and wherein the rate of ingotwithdrawal is expressed as, R 2 G D tan theta where, R rate of ingotwithdrawal in inches/minute G rate of mold gyration in rpm D diameter ofmold opening in inches theta cone angle.
 3. A method in accordance withclaim 1 wherein said molten metal forms within said ingot a melt havinga meniscus level defining its upper surface and wherein the point ofgyration of said mold is above said meniscus.
 4. Apparatus forcontinuous casting of metal ingot from molten metal comprising, a moldelement having a conical opening extending through it, means forgyrating said mold element about a point on the axis of said conicalopening, such that a portion of the mold side will be continuouslyaligned with the vertical axis of the ingot means for continuoussupplying said molten metal to one end of the opening through said moldelement, and means for withdrawing continuously at a predetermined ratethe solidified ingot from the other end of the opening through said moldelement such that said ingot withdrawal velocity is matched to thedownward vertical movement velocity of said portion of the mold side. 5.Apparatus in accordance with claim 4 wherein said mold element is formedof copper and is water cooled.
 6. Apparatus in accordance with claim 4wherein said mold element is constrained from rotating about the axis ofsaid conical opening when said element is gyrating.
 7. Apparatus inaccordance with claim 4 wherein said mold element is positioned so thatsaid conical opening is generally vertical.
 8. Apparatus in accordancewith claim 4 and further including means controlling the rate ofgyration of said mold element to a first velocity and controlling therate of withdrawal of said ingot, said means for controlling beingarranged so that the relationship between the rate of withdrawal of saidingot and the rate of gyration of said mold is R 2 G D tan theta where,R rate of ingot withdrawal in inches/minute G rate of mold gyration inrpm D diameter of mold opening in inches theta cone angle.
 9. Apparatusin accordance with claim 4 and further including a base member, saidmeans for gyrating said mold element comprising a rotatable cam elementof varying thickness supporting said mold element upon said base elementand, means for rotating said cam thereby producing the gyration of saidmold.